This research proposes a series of integrated studies to elucidate the importance of the metabolic activation of procarcinogens by human cytochrome P4501B1 (CYP1B1), a potential susceptibility factor for chemical carcinogenesis. The long-term goal of this research is to determine the contribution of CYP1B1 to human cancers that result from exposure to chemical carcinogens found in the diet, tobacco smoke and the environment. The specific aims of this study are to: 1) Determine the metabolic activity of human CYP1B1 towards benzo[a]pyrene (BP), 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), pyrene and caffeine; 2) Identify genetic polymorphisms (allelic variants) of human CYP1B1; and, 3) Determine the level of CYP1B1 protein in samples of human colon, intestine, lung, liver, kidney and breast. BP and PhIP are widespread procarcinogens known to be metabolized by the other CYP1 enzymes, CYP1A1 and CYP1A2. Pyrene is a co-carcinogen that is often used as a marker of human PAH exposure. Caffeine metabolism is commonly used to phenotype human CYP1A2 content. The metabolic profile of human CYP1B1 will be determined using yeast expressing recombinant human CYP1B1, and human cell lines expressing CYP1A1, or CYP1A2, or CYP1B1. Specific metabolites will be identified by high pressure liquid chromatography (HPLC) and synchronous fluorescence spectroscopy (SFS). Variants of other CYP genes have been associated with the occurrence of specific human cancers. Allelic variants of the CYP1B1 coding region will be identified by polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) analysis of a panel of human DNAs. The relevance of identified variants will be investigated using a yeast CYP1B1 expression system. The proposed studies of CYP1B1 protein will provide important new information about the expression of this enzyme in human tissues.